Never cast a clout until May is out

Do you know the meaning of this? "Hasta el 40 de mayo no te quites el sayo".
Idioms, idioms, idioms.....how difficult they are when learning a language!
In Spanish and talking about the weather, everybody has ever heard about it, and everybody knows that in spring obviously you can’t bet on non-stop good weather until at least June 10th,to put in evidence how the good and stable weather can only be found in summer.
And the more idioms you know, the easier you´ll find to communicate in a foreign language. So apart from this, you´ll enjoy differences and similarities when expressing common sayings, because idioms are part of the culture and add colour to language.
Here you are some sites to learn them:
http://www.saberingles.com.ar/idioms/proverbs.html
http://www.idiomsite.com/
Finally, play a game with idioms:
http://www.funbrain.com/idioms/
and if you want to practise more idioms quizzes:
http://a4esl.org/q/h/idioms.html